我想从屏幕外(不受CAEAGLLayer支持)帧缓冲区读取像素。我创建缓冲区的代码如下所示:glGenFramebuffersOES(1,&_storeFramebuffer);glGenRenderbuffersOES(1,&_storeRenderbuffer);glBindFramebufferOES(GL_FRAMEBUFFER_OES,_storeFramebuffer);glBindRenderbufferOES(GL_RENDERBUFFER_OES,_storeRenderbuffer);glFramebufferRenderbufferOES(GL_FRAMEBUFF